1. Field Of The Invention
The invention relates to a petroleum refining process. More particularly, the invention relates to a delayed coking process for converting a high sulfur, residual oil feedstock to coke and hydrocarbon liquids and gases. Most particularly the invention relates to separating and desulfurizing liquid and gaseous products of delayed coking.
2. Description Of Other Related Methods In The Field
In a delayed coking process, a heavy liquid hydrocarbon fraction is converted to solid coke and lower boiling liquid and gaseous products. The fraction is typically a residual petroleum based oil or a mixture of residual oil with other heavy fractions.
In a typical delayed coking process, the residual oil is heated by exchanging heat with liquid products from the process and is fed into a fractionating tower wherein light end products are removed from the residual oil. The oil is then pumped from the bottom of the fractionating tower through a tube furnace where it is heated under pressure to coking temperature and discharged into a coking drum.
In the coking reaction the residual feedstock is thermally decomposed into solid coke, condensable liquid and gaseous hydrocarbons. The solid coke is recovered. Coke quality determines its use. High purity coke is used to manufacture electrodes for the aluminum and steel industry. Lower purity coke is used for fuel; its value calculated based on the sulfur and heavy metal impurities which are transferred from the feedstock to the coke.
The liquid and gaseous hydrocarbons are removed from the coke drum and returned to the fractionating tower where they are separated into the desired hydrocarbon fractions.
U.S Pat. No. 4,332,671 to L. D. Boyer teaches a delayed coking process in which a heavy high-sulfur crude oil is first atmospheric distilled and then vacuum distilled to produce feedstock for delayed coking. Vapor and liquid products of delayed coking are subjected to hydrotreating to yield lower sulfur liquid and gas products.
U.S. Pat. No. 3,907,664 to H. R. Janssen et al. teaches a control system for a delayed coker fractionator. In particular, a coker fractionator overhead vapor fraction is condensed. The uncondensed vapor is passed from the accumulator to gas recovery. A portion of the condensed liquid is used to reflux the coker fractionator. The remaining portion of condensed liquid is passed to gas recovery.
U.S. Pat. No. 4,686,027 to J. A. Bonilla et al. teaches a delayed coker process. An overhead fraction from the coker fractionator is cooled, compressed and passed to an absorber/stripper. The vapor product of the absorber/stripper is a fuel gas stream. Fuel gas typically comprises methane and ethane.
The liquid product of the absorber/stripper is passed to a stabilizer which produces a C.sub.3 /C.sub.4 overhead product and total naphtha as a bottoms product.